This invention relates to rearview mirrors of the type employed by automotive vehicles, and more specifically to a family of mirrors formed in accordance with certain structural, geometrical and mathematical relationships to provide a wide field of view of objects in the rear and along side of the vehicle by providing a controlled distortion of the viewed objects, and minimizing the effects of bi-ocular vision of the image of an object in a mirror having a compound curve of variable radius.
Many rearview mirrors in automotive vehicles, as well as the side mirrors, provide a compromise between several conflicting factors. To obtain a relatively large and accurate image of other vehicles moving in the rear, as well as along both sides of the observer's vehicle obviously calls for a relatively large mirror, the larger the mirror, the better the field of view. However, large mirrors interfere with the observer's forward vision through the windshield, as well as oblique vision beyond side view mirrors.
Another problem is that a flat mirror provides only a limited view of vehicles along side the observer's vehicle. One answer is to provide a compound convex mirror having a relatively flat primary viewing surface for viewing objects to the rear of the vehicle, and increasingly curved mirror ends for extending the observer's view of side objects. This approach, however, presents several problems. Since the mirror ends are convex, there usually is considerable image distortion depending upon the curvature of the mirror, and other geometric considerations. Some of the distortion has been reduced in the prior art, but by sacrificing image size, for example U.S. Pat. No. 4,012,125 issued to Philip J. Hart. Other approaches have utilized various conic sections curves and other empirically derived curves in attempts to make an acceptable transition between the primary and edge viewing surfaces. Without exception, results are mirrors having optical distortions because of the observer's bi-ocular vision. In most cases, extremely severe bi-ocular distortions are instantaneously generated at the transition line between different geometric curvatures of the mirror. These basic problems occur in some mirrors having a compound curvature when one eye of the observer is viewing an object through one curvature, and his other eye is viewing the same object through a portion of the mirror having a different curvature. This bi-ocular problem becomes aggravated when the observer is viewing a moving object having an image progressively passing through several curvatures.
My co-pending application, Ser. No. 916,598, utilizing a continuous function modified cycloidal geometry, provides a solution for this type of mirror in which the mirror has a relatively flat primary central viewing surface for viewing objects to the rear of the observer, and a peripheral curved end portion having a curvature continuously decreasing from the primary mirror portion surface. Such a mirror, with properly selected and proportioned geometric curvature sections, provides a useful balance between a unit image or zero distortion image and a wide field of vision.